Comment on “The Bay of Naples (southern Italy): Constraints on the volcanic structures inferred from a dense seismic survey” by S. Judenherc and A. Zollo

Abstract

[1] The recent paper by Judenherc and Zollo [2004] reports the results of a seismic experiment focused on the Bay of Naples. They propose a model of the Campi Flegrei caldera in relation to the underlying Mesozoic limestone unit. According to the authors (paragraph 1), “two NE-SW normal faults run beneath the Vesuvius volcano and Campi Flegrei, which are related to the pre-Pleistocene Apenninic tectonics.” In particular (paragraph 25), “from the Sorrentine Peninsula toward the central Bay of Naples the model shows two remarkably linear structures that they interpret as a two-step deepening of the carbonatic layer.” They affirm that the southernmost step is well known from literature (i.e., the offshore continuation of the Torre del Greco fault), while the other fault, NE striking and located to the SE of the Campi Flegrei caldera (paragraph 30) “has never been observed before.” However, apart from the fact that a structural model of the bay based on the deepening of the carbonate basement by normal faults is well known since “70th” [Finetti and Morelli, 1974], Bruno et al. [2003] reported the presence of this specific fault (which they called Magnaghi-Sebeto Fault) and discussed its volcanologic implications. Bruno et al. [2003, p. 193] wrote that “a main alignment of conjugate NE–SW faults, named here as ‘Magnaghi–Sebeto line’, intersects several submarine volcanic banks and separates the bay into two sectors, characterized by important geological, geophysical and petrochemical differences.” Such a separation of the bay in two geophysical and volcanologically different sectors was also evidenced by the analysis of the magnetic and gravity anomaly map by Florio et al. [1999]. [2] Moreover, Judenherc and Zollo [2004, paragraph 26] individuate a ring-like high-velocity object in the Campi Flegrei area and associate it to the caldera of Campi Flegrei. They also suggest (paragraph 1) that “the feeding system of the Campi Flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the Bay of Naples.” In this case, previous scientific articles [e.g., Orsi et al., 1996; D'Antonio et al., 1999; Florio et al., 1999; Bruno, 2004; De Astis et al., 2004] have also shown and discussed the shape and extension of the Campi Flegrei caldera and the relationships between volcanic structures and tectonic lines using geochemical, volcanological, mesostructural, seismic reflection, and potential field data. [3] For example, Orsi et al. [1996] remark that the caldera resurgence is controlled by NE-SW faults; D'Antonio et al. [1999] discuss the influence of NE-SW structural patterns on magma ascent; Bruno [2004] writes that the caldera collapse in the marine sector of Campi Flegrei is strongly controlled by regional NE–SW and NW–SE structural discontinuities; Florio et al. [1999] in particular define and discuss the shape and extension of the caldera by processing aeromagnetic and gravity data by boundary analysis techniques. Finally, De Astis et al. [2004] infer by petrological and volcanological data that volcanism at Procida, Ischia, and Campi Flegrei is controlled by NE structural faults. [4] No correct mention of these previous works, relevant to the conclusions and interpretation presented by Judenherc and Zollo, has been made by them in their article. I am afraid this may cause embarrassment within the geophysical-volcanological scientific community working on the area. I hope that this short communication may allow readers to correctly compare models and hypotheses on the origin of the volcanism in the Campi Flegrei area.